illumination filters / accessories resource guide
cameras liquid lens / specialty telecentric fixed focal length
microscopy /
objectives
Camera Resolution by Pixel Size
Pixel Size (μm) 9.9 7.4 5.86 5.5 4.54 3.69 3.45 2.2 1.67
Resolution (lp/mm) 50.5 67.6 85.3 90.9 110.1 135.5 144.9 227.3 299.4
Typical 1/2" Sensor (MP) 0.31 0.56 0.89 1.02 1.49 2.26 2.58 6.35 11.02
Typical 2/3" Sensor (MP) 0.59 1.06 1.69 1.92 2.82 4.27 4.88 12.00 20.83
Table 10.2: Camera Resolution by Pixel Size.
CCD vs. CMOS Sensors
CCD CMOS CCD CMOS
Pixel Signal: Electron Packet Voltage Uniform: High Moderate
Chip Signal: Analog Digital Resolution: Low-High Low-High
Fill Factor: High Moderate Speed: Moderate-High High
Responsivity: Moderate Moderate-High Power Consumption: Moderate-High Low
Noise Level: Low Low to High Complexity: Low Moderate
Dynamic Range: High Moderate to High Cost: Moderate Low
Table 10.3: CCD vs. CMOS Sensors.
Section 10.5: Spectral Properties
Depending on an application’s requirements, a camera’s ability to reproduce
color may or may not be beneficial. A comparison of monochrome,
single chip color, and three chip color cameras is shown in
Table 10.4 and more detail is provided in the following section.
Monochrome vs. Color
Monochrome Color (Single Chip) 3 Chip Color Cameras
• Single Sensor Outputs
Grayscale Images
• Uses RGB Bayer Color Filter
(Typical)
• Utilizes a Prism to Split White
Light into 3 Different Sensors
• 10% Higher Resolution
than Comparable
Single-Chip Color Cameras
• Lower Resolution
(More Pixels Required
To Recognize Color)
• More Costly
• Better Signal-To-Noise Ratio;
Greater Contrast • Better Color Resolution
• Increased Low-light Sensitivity • Smaller Selection of Lenses
• Mag Require Specially
Designed Lenses
Table 10.4: CCD vs. CMOS Sensors.
146 +44(0) 1904 788600 | Edmund Optics® targets Normalized Response of a Typical Monochrome CCD
400 500 600 700 800 900 1000 1100 1200
Wavelength (nm)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Relative Spectral Response
with IR cutoff filter without IR cutoff filter
Figure 10.2
Figure 10.2: Normalized Spectral Response of a Typical Monochrome
CCD.
Monochrome Cameras
CCD and CMOS sensors, being silicon devices, are sensitive to wavelengths
from approximately 350 - 1050nm, although the usable range
is usually given from 400 - 1000nm. This sensitivity is indicated by the
sensor’s spectral response curve (Figure 10.2). However, most highquality
color, and some monochrome, cameras provide an infrared
(IR) cut-of filer for imaging specifically in the visible spectrum.
Color Cameras
The solid state sensor is based on the photoelectric effect and, as a
result, cannot distinguish between colors without additional considerations.
There are two types of color CCD cameras: single chip and
three-chip. Single chip color CCD cameras offer a common, low-cost
imaging solution and use a mosaic (e.g. Bayer) optical filer to make
different pixels sensitive to only certain wavelengths of light. A color
image is then reconstructed in software using a “de-bayering” algorithm
which interpolates true color information from the RGB signals.
Since more pixels are required to recognize color, single chip color
cameras inherently have lower resolution than their monochrome
counterparts. Three-chip color CCD (3CCD) cameras are designed to
solve this resolution problem by using a prism to direct each section
of the incident spectrum to a different chip. Although 3CCD cameras
typically provide extremely high resolutions and more accurate color
reproduction, they have lower light sensitivities and can be costly.
Frame Rate and Shutter Speeds
The frame rate refers to the number of full frames composed in a
second. In high-speed applications, it is beneficial to choose a faster
frame rate to acquire more images of the object as it moves through
the FOV. The shutter speed corresponds to the inverse of the exposure
time of the sensor. The exposure time controls the amount of
A: Stationary B: Global Shutter
C: Rolling Shutter
Figure 10.3: Comparison of Motion Blur. Stationary PCB (A) and
images of moving PCB with Continuous Global Shutter (B) and Rolling
Shutter (C).
incident light collected by the sensor. Camera blooming (caused by
over-exposure) can be controlled by decreasing illumination, or by
increasing the shutter speed (decreasing exposure time).
The maximum frame rate for a system depends on the sensor readout
speed, the data transfer rate of the interface, and the number of
pixels (amount of data transferred per frame). Often, a camera may be
run at a higher frame rate by reducing the resolution by binning pixels
together or restricting the area of interest. For digital cameras, exposures
can be made from tens of microseconds to minutes, although
the longest exposures are generally only practical with CCD cameras,
which have lower dark currents and noise compared to CMOS.
Electronic Shutter: Global vs. Rolling
A global shutter is analogous to a mechanical shutter, in that all pixels
are exposed and sampled simultaneously, with the readout then occurring
sequentially; the photon acquisition starts and stops at the
same time for all pixels. On the other hand, a rolling shutter exposes,
samples, and reads out sequentially; it implies that each line of the
image is sampled at a slightly different time. Intuitively, images of